1. Field of the Invention
The present invention relates to the storage and transmission of digital data by a new pulse code modulation technique. An encoder is provided to change the signals from NRZ encoded format into the new pulse code modulation format. A decoder is provided to change the encoded signals from the new format back into the NRZ encoded format.
2. Description of the Prior Art
A delay-modulation code sometimes known as the Ampex-Miller code is described in an article contained in the Electronic Design 21, Oct. 11, 1975 issue. A differential pulse code modulation technique is described in U.S. Pat. No. 3,988,729.
The present encoding and decoding technique differs from the Miller encoding format because the Miller encoded signal always has a transition in the middle of a data cell when the NRZ signal to be encoded represents a binary one. The encoding and decoding technique of the present invention does not follow this encoding format. According to the encoding procedure hereinafter described a binary one in the NRZ signal to be encoded can be represented in one of two ways, namely: first, a transition in the encoded waveform can be found in the middle of a data cell; or second, a transition in the encoded waveform can occur at transition time between data cells.
U.S. Pat. No. 3,988,729 teaches that transitions in the encoded waveform occur in the center of a data cell time for either a binary one or binary zero in the NRZ format. The signals encoded according to the procedure hereinafter described, include signal level transitions occurring in the center of a data cell time only for a binary zero in the NRZ format.